when I play on the virtual pinball machine it happens that sometimes the power turns off, and there I know that it is the diode that is dead.
I take out the diode and I test it and there I find that it is conductive in both directions.
Okay, that makes sense - that's consistent with having it installed correctly.
I always connect my contactors with relay card, this photo is just found on google image.
Good! I was worried when I saw that diagram together with "4A contactor". It's really the LedWiz that would have blown out in that scenario, not the diode, so it didn't seem like it could possibly be what was going on, but I figured I'd ask.
If the 4007 series are blowing consistently then you are exceeding 1A in the flyback voltage being generated.
Not just that, it means you're exceeding *30* Amps - the surge current rating for the 1N4007.
Which is what makes me think you might have something else going on here that's going to make any diode you install blow, no matter how large it is. (Like I said, the 1N4007 is used for even beefier coils in real pinball machines, so why is it blowing with these?) That was why I asked how you know the diodes are dead: if the answer was "because the contactors stop working", I was going to guess that you had the diodes wired in series with the contactors so that they were carrying the fully 4A load every time the contactors turned on. But it sounds like you have them wired right based on your symptoms, so maybe there's something else besides that something else.
One thing you could try is to insert a small resistor in series with the diode - maybe something on the order of 5 to 20 ohms (not "K" ohms, just plain ohms). That would limit the flyback current going through the diode. (But you want to keep that added resistance as small as possible, because the whole point is to provide a low-resistance local loop for the flyback.)
Coil(+) ---- 5 ohm ---- |<Diode----- (-) Coil
Edited by mjr, 14 December 2019 - 07:12 PM.